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Rearranging a formula

For the formula:

Screenshot.png


I have to make a the subject. What is the right answer? Please explain HOW you get the correct answer with working out. Thanks.

I got:
a=8-4c
44-----
444b-c

But I got the wrong answer:confused:
Reply 1
Avatar for raheem94
raheem94
13
Original post by krisshP
For the formula:

Screenshot.png


I have to make a the subject. What is the right answer? Please explain HOW you get the correct answer with working out. Thanks.

I got:
a=8-4c
44-----
444b-c

But I got the wrong answer:confused:


Its not allowed to post full solutions.

Can you show your working, then i can tell you where you went wrong.
Reply 2
Avatar for TLK
TLK
8
Original post by krisshP
For the formula:

Screenshot.png


I have to make a the subject. What is the right answer? Please explain HOW you get the correct answer with working out. Thanks.

I got:
a=8-4c
44-----
444b-c

But I got the wrong answer:confused:


You forgot to multiply ab by 4 when getting rid of the fraction.
Reply 3
Avatar for krisshP
krisshP
OP
14
when multiplying ab by 4 I get a wrong answer of

8-4c
-------=a
4b-c

Here I first multiplied by 4 and expanded to get:
4ab-ca+4c=8
Then I -4c to get:
4ab-ca=8-4c
After this I factorised the LHS to get:
a(4b-c)=8-4c
Then I divided both sides by (4b-c) to get the answer stated above.

WHY did I fail?
Reply 4
Avatar for TLK
TLK
8
Original post by krisshP
when multiplying ab by 4 I get a wrong answer of

8-4c
-------=a
4b-c

Here I first multiplied by 4 and expanded to get:
4ab-ca+4c=8
Then I -4c to get:
4ab-ca=8-4c
After this I factorised the LHS to get:
a(4b-c)=8-4c
Then I divided both sides by (4b-c) to get the answer stated above.

WHY did I fail?


What is the final answer supposed to be?
Reply 5
Avatar for raheem94
raheem94
13
Original post by krisshP
when multiplying ab by 4 I get a wrong answer of

8-4c
-------=a
4b-c

Here I first multiplied by 4 and expanded to get:
4ab-ca+4c=8
Then I -4c to get:
4ab-ca=8-4c
After this I factorised the LHS to get:
a(4b-c)=8-4c
Then I divided both sides by (4b-c) to get the answer stated above.

WHY did I fail?

ab−c(a+4)4=2 \displaystyle ab - \frac{c(a+4)}{4} = 2

Multiply throughout by 4,
4ab−c(a+4)=8[br]4ab−ac−4c=8 \displaystyle 4ab - c(a+4) = 8[br]\displaystyle 4ab - ac -4c =8
Reply 6
Avatar for krisshP
krisshP
OP
14
Not sure but I know that the answer of:

8-4c
------ = a
4b-c

is wrong.

What answer do you get? Is it the same as if it is it could mean that mymaths is wrong.
Reply 7
Avatar for raheem94
raheem94
13
Original post by krisshP
Not sure but I know that the answer of:

8-4c
------ = a
4b-c

is wrong.

What answer do you get? Is it the same as if it is it could mean that mymaths is wrong.


I have indicated your mistake in my previous post.
Reply 8
Avatar for krisshP
krisshP
OP
14
Thanks Raheem94 for making me learn from a mistake :smile::smile::smile:
Reply 9
Avatar for raheem94
raheem94
13
Original post by krisshP
Thanks Raheem94 for making me learn from a mistake :smile::smile::smile:


You are welcome.

By the way, what answer do you get, so that i can confirm if you are right or wrong.
(edited 12 years ago)
Reply 10
Avatar for krisshP
krisshP
OP
14
I entered the new answer on mymaths and I got a tick, so the new answer was correct :smile::smile::smile:
Thanks
(edited 12 years ago)

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